Document handlers are devices which draw individual sheets from a stack of sheets, and sequentially allow the image on each sheet to be recorded, typically by a photoreceptor (in a “light-lens” or analog copier) or by a photosensitive device (in a digital copier, scanner, or facsimile). In a common arrangement, a copier has a conventional main platen, on which single sheets can be manually placed, as well as a smaller platen, typically adjacent the main platen, which is used by the document handler when sheets are being passed therethrough. In a typical design, when a single sheet is being recorded through the main platen, the photosensitive device (or “scan head”) is moved relative to the platen to record the entire image; when the document handler is being used to expose images through the smaller platen, a photosensitive device is typically left stationary under the smaller platen, and the motion of the sheet caused by the hardware within the document handler provides the necessary relative motion of each sheet past the photosensitive device.
For recording images on sheets which bear images on both sides thereof, there has typically been two general approaches. For scanners with a single scan head, the general approach is to use the scan head first to scan one side of the sheet, and then mechanically invert and re-feed the sheet so that the other side of the sheet is moved past the scan head. For scanners with two scan heads, each scan head is effectively placed on opposite sides of a paper path, so that both images on both sides of the sheet are recorded.
In the two-scan-head case, a practical challenge relates to the fact that each of the two scan heads will in effect emit image data, possibly simultaneously, as a single sheet is being recorded. To accommodate this dual output of page image data, the downstream circuitry for processing and recording the image data must be designed accordingly. For various practical reasons, however, it is often preferable to retain a processing architecture (regarding both software and electronic hardware) which “handles” one page image at a time.
The present disclosure relates to a mechanical architecture for a two-scan-head document handler which takes into account the above-mentioned considerations.